1. Field of the Invention
The present invention relates to a liquid crystal display having a structure for preventing temperature rises of a liquid crystal panel and an optical member, and a light source device used for the same.
2. Description of the Related Art
In recent years, as a size of a liquid crystal display has been made larger, a desire has been strong for a liquid crystal display having a high brightness and a widely visible angle. In order to attain the liquid crystal display having the.high brightness, it is tried to increase a transmittivity of the liquid crystal panel and improve light usage efficiency. However, since they have limits, an approach of increasing a brightness of a back-light, namely a light source is typically tried.
Also, with regard to the attainment of the widely visible angle, there may be a case that the transmittivity of the liquid crystal panel is sacrificed. In order to compensate this demerit, it is effective to employ a technique for increasing the brightness of the light source.
Thus, the attainment of the higher brightness of the light source gives the sufficient effect to the high brightness and the widely visible angle of the liquid crystal display.
However, as mentioned above, the increase in the brightness of the light source requires an increase in an input power to a light source device. When an attention is paid to the light emission mechanism of the light source, it is typically known that several tens of percents of energy supplied to the light source device are lost as heat. That is, associated with the increase in the input power to the light source, the heat loss is increased, and a calorific value of the light source is increased.
As the calorific value of the light source is increased, a temperature of a liquid crystal panel mounted near the light source device is also raised. Since this liquid crystal panel depends on a temperature characteristic of itself, there may be a fear of a drop in a display quality as the liquid crystal display. Thus, such a liquid crystal display is desired that can attain the high brightness without any drop in the display quality of the liquid crystal panel.
For solving such a problem, a structure is employed in which a fan or a heat sink is mounted on a rear of a body of the liquid crystal display.
A conventional liquid crystal display and a light source device used for the same will be described below with reference to the attached drawings.
FIG. 1A is a perspective view showing a configuration of a conventional liquid crystal display. As shown in FIG. 1A, a liquid crystal display 1 is composed of a body 3 in which a liquid crystal panel 2, a light source device (not shown) and the like are built in, a radiator 7 mounted on a rear of the body 3, and a substrate part 8.
An opening portion 31a is positioned on a shield front 31 constituting a surface side of the body 3. A part of a surface of the liquid crystal panel 2 is exposed in the opening portion 31a, and the exposed portion forms a display surface of the liquid crystal display 1.
Also, the radiator 7 is directly mounted in a shield rear (not shown) constituting the rear side of the body 3. As the material for this shield rear, aluminum having high heat conduction and a lightweight are used in many cases.
In this way, the heat radiated from the light source device is released through the shield rear having the high heat radiate-ability to external portion.
Here, the surface of the liquid crystal panel 2 implies the display surface of the liquid crystal panel 2. Hereinafter, with regard to the description of surfaces besides the liquid crystal panel 2, a plane positioned in a direction similar to the surface of the liquid crystal panel 2 is noted as a surface, and a plane on a rear of the surface is noted as a rear.
The inner structure of the liquid crystal display will be described below with reference to FIG. 1B showing a section taken on the line Axe2x80x94Axe2x80x2 of FIG. 1A. As shown in FIG. 1B, in the liquid crystal display 1, the liquid crystal panel 2 having a form of substantial plate, an optical member 5, such as a diffusion plate or the like, and a light source device 4 are substantially parallel and opposite to each other. The liquid crystal panel 2 is put between a shield front 31 and a shield center 32. The optical member 5 and the light source device 4 are put between the shield center 32 and a shield rear 33. Also, the radiator 7 and the substrate part 8 are mounted on the rear of the shield rear 33.
The structure of the light source device will be described below with reference to FIGS. 2A and 2B. As the structure of the light source device 4, there are mainly a straight fall type structure and a side light type structure. FIG. 2A is a section view showing a liquid crystal display having a light source device of the straight fall type structure, and FIG. 2B is a section view showing a liquid crystal display having a light source device of the side light type structure.
As shown in FIG. 2A, in the light source device 4 having the straight fall type structure, a reflector 43 is mounted inside a substantially dished portion (hereafter, referred to as xe2x80x9clamp housexe2x80x9d) of the shield rear 33. Near a reflector 43, a plurality of light sources 41 are mounted along the reflector 43 in parallel. Each of the plurality of the light sources 41 is cylindrical in shape. Also, the optical member 5, such as a diffusion plate or the like, is mounted on a light emission side of the light source device 4 having the straight fall type structure so as to cover the lamp house by keeping a predetermined distance from the light source 41, in order to avoid an occurrence of irregular brightness.
As shown in FIG. 2B, the light source device 4 having the side light type structure is composed of a light guide plate 42 having a form of substantial plate, a light source 41 that is mounted on one side of the light guide plate 42 and is cylindrical in shape, and a reflector 43 mounted so as to surround the light source 41 together with one side of the light guide plate 42.
The light guide plate 42 is made of acrylic having a high light transmittivity and the like. A light from the light source 41 is transmitted through the light guide plate 42, and radiated to the rear of the liquid crystal panel 2 from a region of an opening portion 32a of the shield center 32, in the surface of the light guide plate 42. Also, the gradation process in which a dot for adjusting the irregular brightness and the like are printed is performed on a plane opposite to a light emission surface in the light guide plate 42, namely, the rear of the light guide plate 42 opposite to the shield rear 33 through the reflector 43.
As the radiation structure of the conventional liquid crystal display, Japanese Laid Open Patent Application (JP-A-Showa, 61-172181) discloses a technique for radiating heat in a light source device by forming a ventilation port in a lamp house and sending air to the ventilation port, in a liquid crystal display having a light source device of a straight fall type structure.
Concretely, as shown in FIG. 3, a lamp house 4a is formed in a light source device 4 mounted on a rear side of a printed circuit board 34 equipping a liquid crystal panel 2. A light source 41 cylindrical in shape is mounted in this lamp house 4a. Also, ventilation ports 44 are formed on an upper side and a lower side of the lamp house 41.
FIG. 4 is a section view when the light source device 4 shown in FIG. 3 is applied to the liquid crystal display. As shown in FIG. 4, an optical member (diffusion plate) 5 is mounted so as to cover the lamp house 4a, and the liquid crystal panel 2 is mounted so as to be opposite to the light source 41 through the optical member 5.
As described above, it is obvious that if a brightness of a display surface in the liquid crystal display is improved, a heat radiation caused by the improvement of the brightness is induced from the light source device to the liquid crystal panel. Thus, an amount of the heat radiation from the light source device to the liquid crystal panel is set in such a range that the amount is equal to or greater than a level which does not drop the brightness of the conventional liquid crystal panel and equal to or less than a level which does not extremely drop a display function.
However, in the heat radiation structure of the liquid crystal display in which the radiator member is mounted on the rear of the body, there are only rooms for the improvement of the heat radiation, such as the employment of the material having the high heat conduction as the material constituting the body and the radiator member, or the increase of the surface area of the radiation member.
In the light source device having the straight fall type structure, especially in the above-mentioned light source device disclosed in Japanese Laid Open Patent Application (JP-A-Showa, 61-172181), penetration holes are formed in the lamp house so that the light source is directly cooled by the air flowing through the penetration holes. That is, the heat of the light source is positively escaped to external portion.
However, a brightness of a light source, such as a cold cathode tube or the like, is changed depending on a temperature. Its brightness is low at a room temperature (about 25xc2x0 C.). A high brightness can be obtained at a condition that it is heated up to about 40-odd xc2x0 C.
Here, as disclosed in the Japanese Laid Open Patent Application (JP-A-Showa, 61-172181), if a size of the ventilation hole is made larger in order to improve the heat radiation efficiency, the temperature of the light source is excessively dropped, which may result in a drop in the brightness. Also, there may be a fear that a temperature rise time is made longer from a room temperature (at a time when the light source is turned on) to a suitable temperature (a maximum brightness).
Thus, the heat radiation efficiency must be reduced such that the temperature of the light source is not dropped beyond the necessity. As a result, the temperature of the liquid crystal panel rises. This results in the drop in the brightness of the liquid crystal panel.
As the related technique, Japanese Laid Open Patent Application (JP-A-Heisei, 8-184827) discloses an illuminating apparatus and a liquid crystal display using the same each of which includes an infrared ray reflection layer that is positioned so as to cover a light source and transmits a light from the light source from which an infrared ray is removed, and a fan apparatus for generating an air flow on a light transmission side of the infrared ray reflection layer and suppressing a heat conduction from the light source.
Japanese Laid Open Patent Application (JP-A-Heisei, 9-160010) discloses a liquid crystal display in which two light diffusion plates positioned separately from each other are mounted between a transmission type liquid crystal display and a bulb, and a portion between the two light diffusion plates is used as an adiabatic air layer.
Japanese Laid Open Patent Application (JP-A-Heisei, 10-96898) discloses a liquid crystal display in which a hollow ventilation member is mounted on an upper surface side and a lower surface side of a body of a back-light, and a fan is mounted near an end of the ventilation member.
Also, Japanese Laid Open Patent Application (JP-A-Heisei, 11-119216) discloses a liquid crystal display having a liquid crystal module in which a light source for emitting a back-light is mounted on a rear side of a liquid crystal panel. In this liquid crystal display, a heat radiation plate is mounted opposite to a substantially entire surface of a rear of the liquid crystal module and is also in contact with a vicinity of a portion opposite to the light source on the rear of the liquid crystal module.
Moreover, Japanese Laid Open Patent Application (JP-A-Heisei, 11-160688) discloses a liquid crystal display in which a liquid crystal panel is mounted within a housing, and a support member is formed on a base frame side for accommodating therein a back-light, and in order that this support member supports the liquid crystal panel on an inner surface side of the housing, a panel support surface of the support member has a plurality of protrusions so that it is in discontinuous contact with the liquid crystal panel.
The present invention is made for solving the above-mentioned problems. Therefore, an object of the present invention is to provide a liquid crystal display that protects a heat accumulation in a liquid crystal panel without any drop of brightness, and a light source device used in the liquid crystal display.
In order to attain this object, in a liquid crystal display according to a first aspect of the present invention, a light emission surface having a substantially single surface in a light source device is opposite to a rear of a liquid crystal panel or a rear of an optical member through an air layer formed by a spacing member.
Due to this configuration, the rears of the liquid crystal panel and the optical member, such as a diffusion plate and the like is not directly radiated the heat generated from the light source device. Thus, it is possible to prevent in advance the drops in the functions of the optical member and the liquid crystal panel. Especially, in the liquid crystal display using the light source device having the straight fall type structure, a light transmission plate is mounted opposite to the rear of the optical member, and it constitutes a light emission surface of a plane light source, and thereby a lamp house is sealed.
The object of the present invention is to increase a brightness of the light source and a brightness of the liquid crystal panel. Thus, it is necessary to carry out a control so that in order to increase the brightness of the light source, the light source is not cooled beyond the necessity, and a temperature of the liquid crystal panel is not raised by the heat from the light source. That is, the light source is shielded from the air layer by the light emission surface, and it is not directly cooled. Thus, the air layer directly cools the liquid crystal panel.
The above-mentioned configuration can control the temperature of the light source and the temperature of the liquid crystal panel so as to increase the brightness of the liquid crystal display and improve the maintenance of a display quality.
Under the object similar to the above object, a liquid crystal display according to the first aspect of the present invention may be comprised such that a light source device is mounted opposite to a light emission target through a diffusion plate. In this liquid crystal display, an air layer is mounted between the light source device and the diffusion plate, and a light emission surface having a substantially single surface is mounted on a light emission target side of the light source device.
Due to this configuration, the light source device has the light emission surface, and the air layer formed by the spacing member is formed between the light emission surface and the optical member. Thus, the radiation heat of the light source device is not directly emitted from the light source device to the optical member or the liquid crystal panel. Thereby, the radiation heat is suppressed by the air layer. Hence, it is possible to prevent in advance the drops in the functions of the liquid crystal panel and the optical member.
In the liquid crystal display according to the first aspect of the present invention, the air layer can be configured such that the heat radiation member as a spacing member is put between the light emission surface of the light source device and the diffusion plate.
Due to this configuration, the opening portion of the heat radiation member, the light emission surface of the light source device and the rear surface of the optical member constitute the air layer. This air layer suppresses the heat radiation from the light source device to the liquid crystal panel or the optical member. Also, even if a calorific value is increased in conjunction with a larger size of a light source device, a capacity of the air layer can be made larger in conjunction with the increase.
The liquid crystal display according to the first aspect of the present invention can be designed such that the light source device has a light emission surface having a predetermined transmittivity on a light emission side of the light source device having a straight fall type constructor.
Due to this configuration, the light emission surface serves as a part constituting the air layer. A distance between the light source and the optical member (diffusion plate) can be reserved to thereby suppress the irregular brightness. Here, the predetermined transmittivity can be a transmittivity at which a light quantity of the light source is not extremely lost and the light emission surface itself does not have the function of the optical member such as the diffusion plate and the like.
In the liquid crystal display according to the first aspect of the present invention, the light source device can be constituted by a light source device having a side light type structure.
The liquid crystal display according to the first aspect of the present invention can be designed such that one or more penetration holes penetrating an inner circumference surface and an outer circumference surface are positioned in the heat radiation member.
Due to this configuration, the air flows through the air layer so that the air layer can be effectively cooled. Thus, it is possible to effectively radiate the heat accumulated in the air layer caused by the radiation heat from the light source device. Hence, the liquid crystal display can be properly operated.
The liquid crystal display according to the first aspect of the present invention can be designed such that the shape of the penetration hole is tapered. Due to this configuration, convection can be easily generated in the air layer so that the heat radiation can be performed further easily in the air layer.
The liquid crystal display according to the first aspect of the present invention can be designed such that the shape of the penetration hole is set in accordance with the flow route of the air. Due to this configuration, the shape of the penetration hole suitable for the easy inflow and outflow (convection) in the air layer is determined based on the direction in which the liquid crystal display is mounted. For example, the shapes of the penetration holes to be formed on upper and lower surfaces and right and left surfaces of the heat radiation member are respectively determined so as to enable the easy convection. Thus, the further effective heat radiation can be performed in the air layer.
The liquid crystal display according to the first aspect of the present invention can be designed such that one or more grooves penetrating an inner circumference surface and an outer circumference surface are formed in the heat radiation member.
Due to this configuration, the groove and the light emission surface of the light source device, or the groove and the rear of the optical member constitute the penetration hole. Accordingly, the heat radiation structure is configured for making the air flow into or flow out from the air layer.
The liquid crystal display according to the first aspect of the present invention can be designed such that the shape of the groove is tapered. Due to this configuration, the convection can be easily generated in the air layer so that the further effective heat radiation can be performed in the air layer.
The liquid crystal display according to the first aspect of the present invention can be designed such that the shape of the groove is determined in accordance with the flow route of the air. Due to this configuration, the shape of the penetration hole suitable for the easy inflow and outflow (convection) in the air layer is determined in accordance with the direction in which the liquid crystal display is mounted. For example, the shapes of the penetration holes to be formed on upper and lower surfaces and right and left surfaces of the heat radiation member are respectively determined so as to enable the easy convection. Thus, the further effective heat radiation can be performed in the air layer.
The liquid crystal display according to the first aspect of the present invention can be designed such that the heat radiation member and the light source device are molded and integrated into a single unit. Due to this configuration, the number of parts as well as the number of assembling processes can be reduced to consequently reduce a manufacturing cost of the liquid crystal display.
Also, under the object similar to the above object, a light source device according to a second aspect of the present invention is designed such that a protrusion is positioned at a circumference edge of a light emission surface, and one or more penetration holes penetrating an inner circumference surface and an outer circumference surface are positioned in such a protrusion. Due to this configuration, an inner surface of the protrusion, a light emission surface of a light source device and an optical member constitute an air layer, and a penetration hole through which air can flow into or flow out from such the air layer can cool the air layer heated by the light source device.
The light source device according to the second aspect of the present invention can be designed such that the shape of the penetration hole is tapered. Due to this configuration, the convection can be easily generated in the air layer so that the further effective heat radiation can be done in the air layer.
The light source device according to the second aspect of the present invention can be designed such that the shape of the penetration hole is set in accordance with the flow route of the air. Due to this configuration, the shape of the penetration hole suitable for the easy inflow and outflow (convection) in the air layer is determined in accordance with the direction in which the liquid crystal display is mounted. For example, the shapes of the penetration holes to be formed on upper and lower surfaces and right and left surfaces of the heat radiation member are respectively determined so as to enable the easy convection. Thus, the further effective heat radiation can be performed in the air layer.
Also, under the object similar to the above object, a light source device according to a third aspect of the present invention is designed such that a protrusion is positioned at a circumference edge of a light emission surface, and one or more grooves penetrating an inner circumference surface and an outer circumference surface are positioned in this protrusion.
Due to this configuration, the groove and the light emission surface of the light source device, or the groove and a rear surface of an optical member constitute a penetration hole. Accordingly, the heat radiation structure is configured for making the air flow into or flow out from the air layer. Thus, the air flows into or flows out from the thus-formed penetration hole, and the heat is radiated from the air layer heated by the light source device. Hence, it is possible to protect the heat accumulation in the optical member and the liquid crystal panel.
The light source device according to the third aspect of the present invention can be designed such that the shape of the groove is tapered. Due to this configuration, the convection can be easily generated in the air layer so that the further effective heat radiation can be done in the air layer.
The light source device according to the third aspect of the present invention can be designed such that the shape of the groove is set in accordance with the flow route of the air. Due to this configuration, the shape of the penetration hole suitable for the easy inflow and outflow (convection) in the air layer is determined in accordance with the direction in which the liquid crystal display is mounted. For example, the shapes of the penetration holes to be formed on upper and lower surfaces and right and left surfaces of the heat radiation member are respectively determined so as to enable the easy convection. Thus, the further effective heat radiation can be performed in the air layer.